Devices that sample pore water in sediments require pumps with precisely controlled flow rates, often less than 1 ml/min. Some devices use a variety of piston pumps to draw samples to an analyzer or collection device. However, piston pumps are not dependable to provide a constant flow rate for extended periods of time, especially at low flow rates against varying resistance, and they suffer from pulsation of the flow stream.
Osmotic pumps require no electrical power. They are based on the osmotic pressure differential between seawater and saturated salt solutions. However, osmotic pumps cannot be turned on and off, have extremely low flow rates that cannot be effectively controlled.
In addition, currently used underwater sampling devices cannot perform some analyses in-situ. Rather, the sample must be transported to a remote location for performing further analysis. This leads to the possibility of contamination of the sample or loss of analytes, particularly in the case of highly reactive or volatile species.